1. Field of the Invention
The present invention relates to an RFID tag (Radio_Frequency_IDentification) tag which exchanges information with an external device in a non-contact manner. Note that among those skilled in the technical field of the present application, the “RFID tag” used in the present specification is regarded as an internal component (inlay) for the “RFID tag” and so it may be referred to as an “inlay for radio IC tag”. Or this “RFID tag” may be referred to as a “radio IC tag”. Furthermore, this “RFID tag” also includes a non-contact type IC card.
2. Description of the Related Art
Various types of RFID tags that exchange information with an external device represented by a reader/writer by radio in a non-contact manner are proposed in recent years. As a kind of this RFID tag, there is a proposal of an RFID tag having such a structure that a radio wave communication antenna pattern and IC chip are mounted on a base sheet made of plastics or paper and such a type of RFID tag is designed to be used in a mode in which the RFID tag is pasted to an article and information on the article is exchanged with an external device to thereby identify the article.
FIG. 1 is a plan view showing an example of an RFID tag. The figure illustrates a state in which a cover sheet, etc., is removed.
In this RFID tag 10, an antenna pattern 12 is formed on a base sheet 11 and an IC chip 13 is placed on this antenna pattern 12. This antenna pattern 12 is a conductive pattern which operates as a dipole antenna consisting of two mono pole patterns 121, 122 extending sideward from the IC chip 13, ends on the IC chip 13 side of which are electrically connected to the IC chip 13. Furthermore, this antenna pattern 12 is provided with a correction pattern 123 for correction of an antenna characteristic, which bypasses the IC chip 13 and connects two extending sections (which correspond to the two mono pole patterns 121, 122 in the structure shown in this FIG. 1), one end of which is connected to the IC chip 13, of this antenna pattern 12. A circuit for carrying out a radio communication with an external device using the antenna pattern 12 as an antenna is built in this IC chip 13.
FIG. 2 shows a connection structure between the IC chip 13 and antenna pattern 12.
The IC chip 13 and antenna pattern 12 are connected by means of flip chip through bumps 14 and surroundings of the bumps 14 are fixed by an adhesive 15.
Here, when the IC chip 13 and antenna pattern 12 are connected by means of flip chip, the ends of the antenna pattern 12 and the IC chip 13 vertically overlap with each other in areas D shown in FIG. 2, which produces a parasitic capacitance C in those parts. When no measures are taken, this parasitic capacitance C causes an adverse influence on the antenna characteristic (radio communication characteristic). The correction pattern 123 shown in FIG. 1 operates as an inductor L which cancels out the influence of this parasitic capacitance C.
The RFID tag 10 has the basic structure shown in FIG. 1, FIG. 2 and the antenna pattern 12 and circuit chip 13 are further covered with a cover sheet.
In a mode of use of such an RFID tag, there is a possibility of tampering that the RFID tag pasted to an article may be peeled off the article and repasted to another article so as to cause an external device to misidentify the article and purchase an expensive article as a cheap one and there is a demand for a technique of avoiding such tampering.
In view of such a current situation, a technique of destroying the antenna pattern, the RFID tag of which is peeled, to disable communications is proposed (e.g., see US Patent Laid-Open No. 2003/075608, U.S. Pat. No. 6,421,013 and National Publication of International Patent Application No. 2003-524811).
FIG. 3 is a plan view showing an example of an RFID tag having the basic structure which has been explained with reference to FIG. 1, FIG. 2 and with a peeling detection function added. A cover such as a cover sheet is removed in this FIG. 3, too.
In the RFID tag 10 shown in this FIG. 3, as in the case of FIG. 1, an antenna pattern 12 made up of mono pole patterns 121, 122 as a dipole antenna is formed on a base sheet 11 and an IC chip 13 is connected to ends of the two mono pole patterns 121, 122 by means of flip chip. Furthermore, this antenna pattern 12 includes a correction pattern 123 which bypasses the IC chip 13 and connects the mono pole patterns 121, 122.
The descriptions so far are similar to those of the RFID tag shown in FIG. 1, but in the case of the RFID tag shown in FIG. 3, a loop peeling detection pattern 16 is additionally formed on the base sheet 11 in such a way as to surround the antenna pattern 12. Both ends of the loop of this peeling detection pattern 16 are also connected to the IC chip 13 by means of flip chip in a structure similar to the connection structure (see FIG. 2) between the antenna pattern 12 and IC chip 13 and this IC chip 13 includes not only the function of radio communication with an external device using the antenna pattern 12 but also the function of detecting destruction of the peeling detection pattern 16. Here, the peeling detection pattern 16 is made of a material such as silver paste, which is conductive, relatively brittle and destructible. This peeling detection pattern 16 is provided with peeling detection points 161 at several locations on the loop.
In the case of the RFID tag shown in FIG. 3, in addition to the antenna pattern 12 and IC chip 13, the peeling detection pattern 16 is further covered with a cover sheet. The peeling detection points 161 of the peeling detection pattern 16 are strongly bonded to the cover sheet, while parts other than the peeling detection points 161 of the peeling detection pattern 16 are bonded more strongly to the base sheet 11 than to the cover sheet. For this reason, when an attempt is made to peel off the cover sheet, the cover sheet is peeled off with only the peeling detection points 161 of the peeling detection pattern 16 remaining bonded to the cover sheet, the peeling detection pattern 16 is destroyed and the IC chip 13 detects the destruction of the peeling detection pattern 16. This prevents the tampering of this RFID tag 10.
However, in the case of the structure shown in FIG. 3, the peeling detection pattern 16 surrounds the antenna pattern 12 and this peeling detection pattern is also made of a conductor, which produces an adverse effect on the antenna characteristic of the antenna pattern 12, greatly attenuates radio waves emitted from the antenna pattern 12 compared to a case in which the peeling detection pattern 16 does not exist (see FIG. 1), causing a problem that the outreach of radio waves (distance within which a radio communication is possible) is drastically shortened.